(a) The contributions required pursuant to 7.1430 for the purchase of creditable service, with the exception of subsection (b) thereof, shall be computed by multiplying the member’s normal monthly contributions at the time the request for credit is initiated by the number of months of prior service being acquired.

(b) In the case of a member purchasing creditable service pursuant to subsection (b) of 7.1430, the number of months of prior service being acquired shall be multiplied by the monthly contributions he would have made if he had been a member of the fund during the period of prior service being acquired.

(c) In the computation of credit for service for purpose of the Fund 15 days or more of service during any month shall constitute a month of service. Service of less than 15 days during any month shall be disregarded. A year shall mean any period of 12 consecutive months and shall not be confined to a calendar year.

(d) Members failing to qualify for the 30 years maximum retirement benefits may apply unused accrued sick leave on an hour for hour basis for service credits.